Supermassive Black Hole Mimics Smaller Cousins

Scientists have caught a supermassive black hole in a distant
galaxy in the act of spurting energy into a jet of electrons
and magnetic fields four distinct times in the past three
years, a celestial take on a Yellowstone geyser.

This quasar-like "active" galaxy is essentially a scaled-up
model of the so-called microquasars within our Milky Way
Galaxy, which are smaller black holes with as much as ten
times the mass of the sun. This means that scientists can
now use their close-up view of microquasars to develop
working models of the most massive and powerful black holes
in the universe.

"This is the first direct, observational evidence of what
we had suspected: The jets in active galaxies are powered
by disks of hot gas orbiting around supermassive black
holes," said Alan Marscher of the Institute for Astrophysical
Research at Boston University, who led this international
team of astronomers.

Active galaxies are distant celestial objects with exceedingly
bright cores, often radiating with the brilliance of thousands
of ordinary galaxies, fueled by the gravity of a central
million- to billion-solar-mass black hole pulling in copious
amounts of interstellar gas.

Marscher and his colleagues have established the first direct
observational link between a supermassive black hole and its
jet. The source is an active galaxy named 3C120 about 450
million light-years from Earth. This link has been observed
in microquasars, several of which are scattered across the
Milky Way Galaxy, but never before in active galaxies,
because the scale (distance and time) is so much greater.

The jets in galaxy 3C120 are streams of particles shooting
away perpendicularly from the plane of a black hole's
accretion disk, moving at 98 percent of the speed of light.
In microquasars, radio-emitting features become visible in
a jet shortly after X rays from the accretion disk get
dimmer -- as if the accretion disk suddenly flushes into
the black hole and disappears, fueling the jet. These
radio "blobs" then appear to move at faster-than- light
speeds, an illusion caused by their ultra-high speeds and
their orientation with respect to Earth.

Now the team of scientists sees this same phenomenon in 3C120.
Roughly every ten months, the X-ray-emitting accretion disk
around its supermassive black hole becomes suddenly dim, and
a month later the telltale bright spot of radio emission
appears in the jet. Over a three-year period, the team
observed a series of radio blobs floating along the particle
jet like smoke puffs, each time following a dip in the
brightness of X rays from the accretion disk.

"What we are likely seeing is the inner part of the accretion
disk becoming unstable and suddenly plunging into the black
hole," said Marscher. "We detect a 'dip' in the X-ray flux
as the hot gas in the disk disappears after it passes the
event horizon. The remainder of the disk is channeled into
the jets, which we see as a knot of radio emission bubbling
away from the black hole. Slowly the accretion disk fills
with more interstellar gas until about ten months later,
when something disturbs the accretion disk orbit, and the
whole thing flushes and blows again."

Joining Marscher on this observation and analysis are Svetlana
Jorstad of Boston University; Jose-Luis Gomez of the
Astrophysical Institute of Andalucia in Granada, Spain;
Margo Aller of the University of Michigan; Harri Terasranta
of the Helsinki University of Technology; Matthew Lister of
NRAO; and Alastair Stirling of the University of Central
Lancashire, England.

The VLBA is a continent-wide radio-telescope system, with one
telescope on Hawaii, another on St. Croix in the Caribbean,
and eight others in the continental United States. Part of
the National Radio Astronomy Observatory, the VLBA offers
the highest resolving power, or ability to see fine detail,
of any telescope available. The
National Radio Astronomy Observatory is a facility of the
National Science Foundation,
operated under cooperative agreement by
Associated Universities, Inc.

The Rossi Explorer was launched by NASA in 1995 to study
black holes, neutron stars and pulsars. The Rossi Explorer
is operated by NASA Goddard Space Flight Center in
Greenbelt, Md.

The
research on 3C120 was supported by funding from the
National Aeronautics and Space Administration and the
National Science Foundation.